1. Field of the Invention
The present invention relates to a knock determination device and particularly to a knock determination device for an internal combustion engine that determines based on a waveform of a vibration of an internal combustion engine whether the engine knocks.
2. Description of the Background Art
Conventionally, a technique for detecting knocking of an internal combustion engine is known. Japanese Patent Laying-Open No. 2001-227400 discloses a knock control device for an internal combustion engine that can accurately determine whether the engine knocks. The knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2001-227400 includes a signal detector detecting a signal representing a waveform of vibration occurring in an internal combustion engine (or a vibration waveform signal), a occurrence period detector detecting a period as an occurrence period during which the vibration waveform signal detected by the signal detector takes on a value of at least a predetermined value, a peak position detector detecting a peak position in the occurrence period detected by the occurrence period detector, a knock determiner determining whether the internal combustion engine knocks based on the relationship between the occurrence period and the peak position, and a knock controller controlling an operation state of the internal combustion engine in accordance with a determination result of the knock determiner. The knock determiner determines knock (knocking) occurs when the peak position relative to the occurrence period is in a predetermined range.
According to the knock control device for an internal combustion engine disclosed in the publication, a signal representing a waveform of vibration occurring in an internal combustion engine is detected by a signal detector. An occurrence period during which the vibration waveform signal takes on a value of at least a predetermined value and a peak position therein are detected by an occurrence period detector and a peak position detector, respectively. Thus, the knock determiner is allowed to determine whether the engine knocks by detecting the position of the peak in the occurrence period of the vibration waveform signal. According to the knock determination result, the operation state of the internal combustion engine is controlled. When the peak position relative to the occurrence period is in a predetermined range, that is, when a waveform is shown in such a shape that the peak position appears earlier relative to a predetermined length of the occurrence period of the vibration waveform signal, the knock determiner recognizes it as being particular to knocking. Thus, even in a transition state where an operation state of the internal combustion engine abruptly changes or when electric loads are turned on/off, whether or not the internal combustion engine knocks is accurately determined, and the operation state of the internal combustion engine can be controlled appropriately.
However, while the engine knocks, a vibration that is greater in magnitude than a vibration attributed to knocking may sometimes be detected as noise. That is, in some cases a vibration attributed to a fault of a knock sensor or attributed to a vibration of the internal combustion engine itself may be greater in magnitude than a vibration attributed to knocking. In such cases, with the knock control device for an internal combustion engine of Japanese Patent Laying-Open No. 2001-227400, there has been a problem that the engine is erroneously determined as not knocking while the engine actually knocks, based on the fact that the peak position relative to the occurrence period is not within a predetermined range.